Influence of intracrystalline diffusion on the selective catalytic reduction of NO by hydrocarbon over Cu-MFI zeolite

The influence of intracrystalline diffusion on the selective catalytic redu ction of NO by hydrocarbons (propane. ethene) was investigated by using Cu- MFI catalysts of different zeolite crystal sizes. The influence of hydrocar bon as a reductant on the diffusion process was also investigated, employin g kinetic and temperature-programmed desorption studies. In the NO-C3H8-O-2 reaction, the apparent reaction rate of NO conversion into Nz did not depe nd on the zeolite crystal size, which indicates that the reaction is not co ntrolled by intracrystalline diffusion. In the NO-C2H4-O-2 reaction, on the other hand, the apparent reaction rate evidently depended on the zeolite c rystal size; the reaction rate over large crystal Cu-MFI (1.29 mu m) was si gnificantly less than that over a small one (0.09 mu m), which indicates th at the reaction is controlled by intracrystalline diffusion. The larger dif fusion resistance in the NO-C2H3-O-2 reaction was attributed to the slower diffusion rate of ethene in zeolite channels than propane, which was due to much stronger interaction of ethene with Cu-MFI catalyst. Thus, the adsorp tion property of hydrocarbon on the Cu-MFI catalyst is revealed to play an important role in determining intracrystalline diffusivity and the diffusio n influence on the selective reduction of NO over zeolite catalysts. (C) 20 00 Elsevier Science B.V. All rights reserved.